Fuser for electrostatic images



June 10, 1969 J. A. KOLI BAS FUSER FOR ELECTROSTATIC IMAGES Filed Aug. 4, 1967 1N VENTOR. JAMES A. KOL/BAS A TTORNE Y United States Patent US. Cl. 2638 Claims ABSTRACT OF THE DISCLOSURE A belt conveyor, subject to heat deterioration, is provided with an inert heat sink section with a radiant heat lamp flooding the heat sink area, and hooded for directing airto move between the belt and the source of heat.

Cross references to related applications A general environment in which this fuser is employed may be seen in application Ser. No. 627,757 filed Apr. 3, 1967. This invention is useful for any fusing situation wherein apparatus is required for selectively and preferentially heating fusible toner carried by a sheet carrier.

Background of the invention The electrostatic copy process generally employs a flexible carrier sheet upon which a toner material is caused to first adhere by electrostatic attraction, and thereafter by adhesion upon being fixed. Fixing is most usually a heat fusion.

High ambient temperature conditions such as by a heating oven, will cause fusing. All material on the sheet is fused in this manner. For some uses, such for example as making lithographic masters, extraneous pieces of undesired background particles of toner ought not to be fused and held permanently.

In some commercial devices for making fused images, the fusing is done under high intensity infra-red radiation conditions. The heat absorbing characteristic of the dark color toner and phenomenon of mutual effect of heating, will cause the larger masses of the toner to create a temperature build-up at a greater speed than the small particle areas.

Objects to be obtained Thus it is desired to use a high intensity heating and do it quickly in order to fuse the image and not fuse the scattered extraneous particles. This invention is concerned with the provision of apparatus to convey a sheet through a focused infra-red heat source quickly, and avoid the consequences of the heat concentration upon the conveying apparatus.

Uniform heating is a requirement for proper fusing. The speed of a sheet passing through the energy Zone, and the intensity of the energy, can be balanced to cause the proper fusing of desired indicia toner masses, and lack of fusing of stray particles. However, if a nonuniform conveyor condition is introduced, then the balance with respect to one area will not be proper with respect to another. It is critical to provide heating uniformity in the heat focus zone.

There are many ways to transport sheets, such as paper stock. The drawings illustrate one convenient method in the form of multiple spaced belts. A single conveyor belt is another possibility. The belt may be composed into two separate conveyor units, or one unit may detour the heat area. Concentration of infra-red radiation creates good selective fusing conditions, whether or not focusing reflectors are used, but creates the danger of burning the belts, as well as the operational problem of uneven heating. If a single conveyor is employed, then the conveyor 3,448,970 Patented June 10, 1969 may deteriorate under the intense heat conditions, and also the surface of the conveyor may heat nonuniformly, thus causing the operating conditions under the reflector to vary. If the carrier sheet is warmed eXcessively it will cause the unwanted small particles to fuse more easily than if it is cold. If a solid conveyor surface is subject to a spotty heat retention condition, it is difficult to control the ambient temperature.

On the other hand, if a plurality of light weight conveyor belts are employed, as shown in the drawings, then in addition to heat deterioration, the differential heating "by the belts across the conveyed page is emphasized.

It is an object of this invention to eliminate the conveyor belt structure from the area of the radiant energy and substitute a resistant area. This may be empty space or a heat sink surface.

A heat sink is usually considered a body to absorb, or draw away, a large quantity of energy to protect a sensitive area. This invention uses a heat sink, in its preferred embodiment, as a means to produce a uniform transport surface temperature in the heat area, and to keep the uniform temperature within acceptable limits.

During the time when no sheet is passing through the fuser, any radiation will fall directly on the heat sink surface, thereby raising its temperature. When an imaged and toned sheet enters the fuser, it is at room temperature. It, therefore, exists at a lower temperature than does the heat sink surface. Because heat flows from higher to lower temperature, thermal energy transfer will be to the toned sheet rather than from it.

Uniform temperature of the surface requires good thermal conductivity. Because the heat sink surface rests directly in view of the heat source, and a great deal of radiant energy is concentrated upon it, it is desirable that the surface not heat excessively. The surface must, therefore, permit rapid heat loss to take place by re-radiation or by convection. Only by keeping the release rate of heat high, can the equilibrium temperature of the sink surface be kept to a reasonable range. This is a classic function of the heat sink.

Therefore, the invention is concerned with providing a support surface portion of a conveyor system at a uniform equilibrium temperature. The equilibrium temperature is balanced with the rate of carrier sheet travel over the surface, and the fusing temperature of the toner used.

The temperature of the support surface will usually be greater than the fusing temperature of the toner, but the carrier sheet will have a resistance to transmission of thermal energy, and the speed of travel will cause a given area to pass over the heat sink surface before the top surface of the carrier sheet comes to the temperature of the heat sink surface, or transmits enough heat to fuse the undesired particles.

It is another object of the invent-ion to substitute an inert portion of the conveyor by means of an area which cannot be greatly harmed by heat, such as by the provision of a detour section of the belt or by insertion of a heat sink or both. The conveyor, which may be a continuous conveyor diverted or a series of conveyors in contiguous relationship, will cause the conveyed sheet to slide across the inert area and be picked up by the moving conveyor on the opposite side of the heat zone.

It is a further object of the invention to provide a passage of air through the fusing station in order to reduce the ambient air temperature and thus emphasize the radiant heating of the dark image on the light colored sheet carrier.

The invention hereinafter described is understood to be an environment wherein it is attempted to selectively and preferentially fuse desirable areas of heat fusible toner.

Summary of the invention The advantage of this invention is that the radiant power of a fuser may be concentrated in a very small area without concern over the destruction of the associated apparatus.

A further advantage is found in that the sheet carrier itself is kept at a temperature below that which would destroy the useful and desirable characteristics of the sheet, whereas the color-bearing toner is caused to elevate in temperature by reason of absorption of radiant energy.

Description of the drawing FIGURE 1 is a schematic illustration of a sheet conveyor system through a fusing station, and including prior process steps in block diagram; and

FIGURE 2 is a section taken along the line 22 of FIGURE 1.

Description of the preferred embodiment In all useful electrostatic devices there is a means for causing a uniform charge across the surface of a carrier sheet. This station in the known process is indicated in the drawing by a labeled block entitled charger. The carrier sheet is material capable of holding a static charge on its surface, and becomes conductive upon exposure to light. Upon exposure, the sheet will allow any electro static charge on the surface to drain away in the area where it is light struck. Such exposure is done by various techniques, including placing a transparent original sheet against the surface of the carrier sheet and exposing through the original, or by producing an optical image and projecting it upon the carrier sheet. This step in the known process is indicated by a block in the drawing labeled exposure.

Finally, a toner material is applied to the sheet carrier, by a known process device indicated by a block in the drawing labeled toner. The toner material is capable of being attracted to an electrostatic charge on the surface of the sheet carrier. The toner is fusible upon exposure to radiant energy or ambient heat. The toner is applied across the charged and exposed surface, and those areas not discharged by exposure will attract and hold some of the toner material. Then, the toner material is caused to fuse and hence bind to the sheet carrier. In this process a permanent image is perfected. These steps are known in the art and hence are illustrated in this drawing only by three general area blocks, and an arrow line indicating delivery of the properly charged, exposed, and toned sheet onto a conveyor 10 which delivers such toned originals to the apparatus illustrated in the FIG- URE 1 of the drawing.

A drive roller 12 provides a common roller serving the belt conveyor 10, and an internal belt conveyor 14. A toned sheet delivered by the conveyor 10 will be transferred to the belt conveyor 14.

Conveyors 10 and 14 are preferably a plurality of individual narrow belts rather than one wide belt, although the preference is not a limiting requirement.

The belt conveyor 14 has an inert section in the form of heat sink 16. The heat sink 16 is a bar of high thermal conductivity metal and extends across the path of conveyor 14. Bar 16 extends across the width of the conveyor, and in that sense it may be said to be as wide as the maximum size sheet to be transported n the conveyor 14, but is considerably more narrow than the length of the sheet to be transported. Then, by the provision of three rollers 18, 19 and 20, a detour for the belt-conveyor 14 is provided around the bar 16. If the bar 16 is not overly wide, a sheet delivered to the belt conveyor 14 will be pushed over the inert bar 16 to the opposite active portion of the belt 14 and hence is caused to move along the path of travel without hesitation. By use of one conveyor detoured, the conveyor to and from the heat sink is exactly synchronized in surface speed.

The heat sink body in the form of bar 16 preferably has a flat top support surface which lies in a common plane with the fore and aft sections of the belt conveyor 14, and is termed an inert portion of the conveyor in view of the fact that it does not move. The bar 16 has a mass and a coefficient of thermal conductivity which conducts heat from the support surface at a rate greater than air conductivity to keep the support surface at an acceptable low temperature.

A radiant energy source 23 contains a lamp 25 for production of infra-red radiant energy. Lamp 25 is a common item of commerce. In the illustrated preferred embodiment, a reflector 27 surrounds the lamp 25 and causes a focus of the energy to a narrow band extending along the central area of the bar 16 support surface. The support surface should be greater than the actual focus area in order to catch the direct radiation from the front of the lamp as well as the reflector focused energy. Thus, the bulk of the energy output of lamp 25 is concentrated on a narrow band of the support surface.

Nevertheless, the surface does heat the carrier sheet as it passes over the surface, but to a temperature which will permit reasonable sheet travel speed without destruction of the sheet or total fusing of a toner burden under the heat influence of the focused lamp.

A housing 31 covers the lamp area and is provided with an exhaust fan 33 to move air out of the housing 31. By moving the air out in this manner, air is of necessity drawn in, and the air which is drawn in is employed to complete the efficiency of this invention.

The housing 31 is attached to the machine housing 36, and the housing 36 is a restricted area over the top of the conveyor 10 and thus forms an entrance opening 37. The housing has an exit opening 39 for discharge of finished sheets from the fusing process. The radiant energy source 23 is preferably placed close to the entrance 37. The opening 39 is a remote area with respect to both the source 23 and the exhaust fan 33, and air flow in through this opening will not flow to the source 23. There is a strong urge of air in through the opening 37, and this flow of air will act as an air jet. Arrows are shown suggesting the flow of air, some of which flows over the surface of reflector 27 and other portions of the air moving between the reflector and the surface of the belt conveyor 14. Air which enters through opening 39 will flow to the fan 33, but this movement merely assists in keeping the interior of the housing 31 at a low ambient temperature. The air movement which enters directly into the fusing process, is that air which is caused to act on a jet principle entering the entrance 37 and projecting between the reflector 27 and the conveyor 14. This air will keep the ambient temperature of the fusing area sufficiently low, that the action of the air and the heat sink together will prevent scorching of the carrier sheet, and permit a high concentration of radiant energy to act upon the dark heat absorbing toner on the surface of the carrier.

What is claimed is:

1. Apparatus for fusing toner material to a flexible carrier comprising:

a radiant energy source arranged to supply the energy output thereof onto a narrow area only;

a belt conveyor having a path of travel aligned with the narrow .area and having a first portion approaching said area and stopping short thereof, means 'guiding said belt conveyor in a loop around said area, and a second portion receding from said narrow area beginning at a distance from the end of the first conveyor portion, said loop being at a greater distance from said radiant energy source than a straight line connecting said first and second portion; and

the belt conveyor in operation transporting a carrier to, through and from the narrow area with the first and second conveyor portions supporting the carrier .5 during its travel and the carrier passing through said narrow area out of contact with said belt conveyor.

2. Apparatus for fusing toner materials to a flexible carrier comprising:

a heat sink body having a support surface, said body having a geometry and coeflicient of thermal conductivity correlated to conduct heat from said support surface at a rate greater than that obtainable by free convection cooling of thesurface area in T;

a radiant energy source arranged to Supply the energy output thereof to a narrow area of said support surface;

a belt conveyor having a path of travel aligned with said support surface and having a first portion approaching said support surface and a second portion receding from said surface, means guiding said belt conveyor in a loop around said area, said loop being at a greater distance from said radiant energy source than a staright line connecting said first and second portions, the belt conveyor in operation transporting the carrier to, through and from the narrow area, with the first and second conveyor portion supporting the carrier and the carrier passing between conveyor portions supported only on the support surface of the heat sink body; and

whereby heating of the carrier from the rear by conduction from the support surface is maintained uniform in a direction perpendicular to carrier travel, and said belt conveyor means is protected from excess heat as the said toner is caused to fuse 'by absorbed radiant energy.

3. Apparatus as defined in claim 2, further characterized in that:

said heat sink is a bar extending transversely of said path of travel, and

said radiant energy source is focused along said bar.

4. Apparatus for fusing toner materials to a flexible carrier surface comprising:

a support surface;

a radiant energy source positioned to supply the energy output thereof to said support surface;

belt conveyor means having a path of travel aligned with said support surface on two opposed sides thereof; 1

said support surface being the top surface of a heat sink bar extending transversely of said path of travel;

a reflector, said radiant energy source positioned in saidireflector, said reflector and energy source con- 'structed to focus said energy along said bar support surface, said reflector spaced from said path;

a housing over said reflector area with an entrance and an exit opening for said belt conveyor; and exhaust means for evacuating said housing, said openings for said belt conveyor and said exhaust means coordinated to cause air drawn through at least one said opening to act as a nozzle directing air between said reflector and belt;

whereby heating of the sheet from the rear by conduction will be maintained uniform in a direction perpendicular to sheet travel, and said belt conveyor is protected from excess heat as the said toner is caused to fuse by absorbed radiant energy.

5. The method of fusing larger masses of electrostatic toner but not fusing stray background particles, comprismg:

( 1) providing a support surface for a carrier sheet;

(2) focusing a band of radiant energy from a remote source upon said surface;

(3) extracting heat from said surface at a rate greater than obtainable by air convection and allowing the surface to obtain equilibrium;

(4) passing a sheet bearing an unfused burden of fusible toner across said surface at a rate to heat the sheet to a temperature below the fusion temperature of said toner; and

(5) subjecting the sheet surface to the said band of radiant energy as it passes over said surface.

References Cited UNITED STATES PATENTS 2,807,703 9/1957 Roshon 1.7 XR 3,117,030 1/1964 Ions et al. 11717.5 XR 3,245,311 4/1966 Cerasani ct a1 95-1.7 XR

CARLTON R. CROYLE, Primary Examiner. ALLAN D. HERRMANN, Assistant Examiner.

US. Cl. X.R. 34-41, 162; 219216; 263-6 

